[1] : WordNet (r) 2.0

zero hour
     n : the time set for the start of an action or operation

[2] : Moby Thesaurus II by Grady Ward, 1.0

26 moby thesaurus words for "zero hour":
   a-day, d day, h hour, charged moment, contingency, crisis,
   critical moment, crossroads, crucial moment, deadline,
   decisive moment, eleventh hour, emergency, exigency, kairos,
   kairotic moment, moment of truth, nick of time, pass, pinch,
   pregnant moment, psychological moment, strait, target date,
   target day, turning point

Zero Hour >> Z Words
Zero Hour, definition of term: Zero Hour
zero+hour_pag1.html

Zero >> Z Words
Zero, definition of term: Zero
zero_pag1.html

Hour >> H Words
Hour, definition of term: Hour
hour_pag1.html

Zero In >> Z Words
Zero In, definition of term: Zero In
zero+in_pag1.html

Man Hour >> M Words
Man Hour, definition of term: Man Hour
man+hour_pag1.html

Kilowatt Hour >> K Words
Kilowatt Hour, definition of term: Kilowatt Hour
kilowatt+hour_pag1.html

Ampere Hour >> A Words
Ampere Hour, definition of term: Ampere Hour
ampere+hour_pag1.html

Happy Hour >> H Words
Happy Hour, definition of term: Happy Hour
happy+hour_pag1.html

Absolute Zero >> A Words
Absolute Zero, definition of term: Absolute Zero
absolute+zero_pag1.html